linux-kernel - Re: [Patch v8 1/7] sched/pelt: Add support to track thermal pressure

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Date:   Thu, 13 Feb 2020 18:01:14 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, ionela.voinescu@....com,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Zhang Rui <rui.zhang@...el.com>, qperret@...gle.com,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>
Subject: Re: [Patch v8 1/7] sched/pelt: Add support to track thermal pressure

On Thu, Feb 13, 2020 at 5:33 PM Amit Kucheria <amit.kucheria@...aro.org> wrote:
>
> On Wed, Jan 15, 2020 at 1:27 AM Thara Gopinath
> <thara.gopinath@...aro.org> wrote:
> >
> > Extrapolating on the existing framework to track rt/dl utilization using
> > pelt signals, add a similar mechanism to track thermal pressure. The
> > difference here from rt/dl utilization tracking is that, instead of
> > tracking time spent by a cpu running a rt/dl task through util_avg, the
> > average thermal pressure is tracked through load_avg. This is because
> > thermal pressure signal is weighted "delta" capacity and is not
> > binary(util_avg is binary). "delta capacity" here means delta between the
> > actual capacity of a cpu and the decreased capacity a cpu due to a thermal
> > event.
> >
> > In order to track average thermal pressure, a new sched_avg variable
> > avg_thermal is introduced. Function update_thermal_load_avg can be called
> > to do the periodic bookkeeping (accumulate, decay and average) of the
> > thermal pressure.
> >
> > Signed-off-by: Thara Gopinath <thara.gopinath@...aro.org>
> > Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
> >
> > v6->v7:
> >         - Added CONFIG_HAVE_SCHED_THERMAL_PRESSURE to stub out
> >           update_thermal_load_avg in unsupported architectures as per
> >           review comments from Peter, Dietmar and Quentin.
> >         - Updated comment for update_thermal_load_avg as per review
> >           comments from Peter and Dietmar.
> > v7->v8:
> >         - Fixed typo in defining update_thermal_load_avg which was
> >           causing build errors (reported by kbuild test report)
> >
> >  include/trace/events/sched.h |  4 ++++
> >  init/Kconfig                 |  4 ++++
> >  kernel/sched/pelt.c          | 31 +++++++++++++++++++++++++++++++
> >  kernel/sched/pelt.h          | 16 ++++++++++++++++
> >  kernel/sched/sched.h         |  1 +
> >  5 files changed, 56 insertions(+)
> >
> > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> > index 420e80e..a8fb667 100644
> > --- a/include/trace/events/sched.h
> > +++ b/include/trace/events/sched.h
> > @@ -613,6 +613,10 @@ DECLARE_TRACE(pelt_dl_tp,
> >         TP_PROTO(struct rq *rq),
> >         TP_ARGS(rq));
> >
> > +DECLARE_TRACE(pelt_thermal_tp,
> > +       TP_PROTO(struct rq *rq),
> > +       TP_ARGS(rq));
> > +
> >  DECLARE_TRACE(pelt_irq_tp,
> >         TP_PROTO(struct rq *rq),
> >         TP_ARGS(rq));
> > diff --git a/init/Kconfig b/init/Kconfig
> > index f6a4a91..c16ea88 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -450,6 +450,10 @@ config HAVE_SCHED_AVG_IRQ
> >         depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
> >         depends on SMP
> >
> > +config HAVE_SCHED_THERMAL_PRESSURE
> > +       bool "Enable periodic averaging of thermal pressure"
> > +       depends on SMP
> > +
> >  config BSD_PROCESS_ACCT
> >         bool "BSD Process Accounting"
> >         depends on MULTIUSER
> > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> > index bd006b7..5d1fbf0 100644
> > --- a/kernel/sched/pelt.c
> > +++ b/kernel/sched/pelt.c
> > @@ -367,6 +367,37 @@ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
> >         return 0;
> >  }
> >
> > +#ifdef CONFIG_HAVE_SCHED_THERMAL_PRESSURE
> > +/*
> > + * thermal:
> > + *
> > + *   load_sum = \Sum se->avg.load_sum but se->avg.load_sum is not tracked
> > + *
> > + *   util_avg and runnable_load_avg are not supported and meaningless.
> > + *
> > + * Unlike rt/dl utilization tracking that track time spent by a cpu
> > + * running a rt/dl task through util_avg, the average thermal pressure is
> > + * tracked through load_avg. This is because thermal pressure signal is
> > + * weighted "delta" capacity and is not binary(util_avg is binary). "delta
>
> May I suggest a slight rewording here and in the commit description,
>
>    This is because the thermal pressure signal is weighted "delta"
> capacity unlike util_avg which is binary.
>
> It would also help, if you expanded on what you mean by binary in the
> commit description and how the delta capacity is weighted.
>
> > + * capacity" here means delta between the actual capacity of a cpu and the
> > + * decreased capacity a cpu due to a thermal event.
>
> This could be shortened to:
>
> Delta capacity of cpu = Actual capacity - Decreased capacity due to
> thermal event
>

Please ignore. I should have sent this against v9, it was languishing
in my mailbox since v8 and I sent this out by mistake.